Tiny magnetic vortices can transform memory storage into powerful computers.
Magnets generate invisible fields that attract certain materials. A well-known example is refrigerator magnets. Much more important to our daily lives, magnets can also store data in computers. Using the direction of the magnetic field (for example, up or down), microscopic bar magnets can each store a piece of memory as a zero or a one – the language of computers.
Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory want to replace the bar magnets with tiny magnetic vortices. These vortices, as small as a billionth of a meter, are called skyrmions, which form in a sense magnetic materials. They could one day usher in a new generation of memory storage microelectronics powerful computers.
“The bar magnets in computer memory are like shoelaces tied with a single knot; it takes almost no energy to untie them,” says Arthur McCray, a Northwestern University graduate student who works in the Materials Science Division (MSD) from Argonne. And any bar magnets that malfunction due to a malfunction will affect the others.
“Skyrmions, on the other hand, are like shoelaces tied with a double knot. No matter how hard you pull on a strand, the shoelaces will stay tied.” The skyrmions are thus extremely stable to any disturbance. Another important feature is that scientists can control their behavior by changing the temperature or applying an electric current.
Scientists still have a lot to learn about the behavior of skyrmions under different conditions. To study them, the Argonne-led team developed an artificial intelligence (AI) program that works with a high-powered electron microscope at the Center for Nanoscale Materials (CNM), a DOE Office of Science user facility in Argonne. The microscope can visualize skyrmions in samples at very low temperatures. This research appeared in Nano letters.
The team’s magnetic material is a mixture of iron, germanium and tellurium. In terms of structure, this material is like a stack of paper with many sheets. A stack of such sheets is high in skyrmions, and a single sheet can be peeled off the top and analyzed at facilities such as CNM.
“The CNM electron microscope coupled with a form of AI called machine learning allowed us to visualize skyrmion sheets and their behavior at different temperatures,” said Yue Li, a postdoctoral fellow in MSD.
“Our most intriguing finding was that the skyrmions are arranged in a highly ordered pattern at minus 60 degrees Fahrenheit and above,” said Charudatta Phatak, a materials scientist and group leader at MSD. “But as we cool the sample, the skyrmion setup changes.” Like bubbles in beer foam, some skyrmions got bigger, some got smaller, some merged and some disappeared.
At minus 270 the layer reached a state of almost complete disorder, but order returned when the temperature returned to minus 60. This order-disorder transition with temperature change could be exploited in future microelectronics for memory storage.
“We estimate the skyrmion energy efficiency could be 100 to 1,000 times better than current memory in the powerful computers used in research,” McCray said.
Energy efficiency is essential for the next generation of microelectronics. Today’s microelectronics already account for about 10% of global electricity. And that number could double by 2030. More energy-efficient electronics are needed.
“We still have some way to go before skyrmions make their way into future low-power computer memory,” Phatak said. “Nevertheless, this kind of radically new way of thinking about microelectronics is key to next-generation devices.”
In addition to Phatak, Li, and McCray, Argonne authors include Amanda K. Petford-Long, Daniel P. Phelan, and Xuedan Ma. Other authors include Rabindra Basnet, Krishna Pandey, and Jin Hu of the University of Arkansas.
Arthur RC McCray et al, Thermal Hysteresis and Ordering Behavior of Magnetic Skyrmion Gratings, Nano letters (2022). DOI: 10.1021/acs.nanolett.2c02275
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